Traditionally, separate elements such as the driving and positioning shoulder and the counter-weight mentioned above have been fitted to the spindle nose by way of screws which engage axially extending threaded bottom holes in the radial flange of the standardized spindle nose.
In the case of extremely quick-running spindles--up to 20,000 rpm and even more--which today occur for some machine tool applications, the high rotational speed results in centrifugal loads acting on the driving and positioning shoulder and on the counter-weight positioned diametrically opposed thereto. These loads may be so large that the screw joints, due to high bending and shearing stresses, will burst during operation. This can cause the driving and positioning shoulder and the counter-weight to come loose and, due to the very high peripheral speed, be thrown away at very high speed. This presents the potential for serious injuries to personnel and damage to materials.